Stereochemical studies on the biosynthesis of the αβ-didehydro-amino-acid units of mycelianamide, cyclopenin, and cyclopenol

Abstract

Feeding experiments with tyrosine, stereoselectively labelled with tritium at C-3, in Penicillium griseofulvum have shown that formation of the αβ-didehydro-amino-acid units of mycelianamide proceeds with high retention of the pro-R- and virtually complete loss of the pro-S-methylene hydrogen atom of the precursor. Analogous studies were conducted with phenylalanine in Penicillium cyclopium. Incorporation of [3-³H]phenylalanine into the secondary metabolites, cyclopenin and cyclopenol, occurred with >50%(typically 65%) loss of tritium, irrespective of the tritium configuration at C-3. This non-stereospecific loss is attributed to an exchange process preceding entry of the precursors into the secondary metabolic pathway. In accord with this, incorporation of [³H]phenyl-alanine into mycelial protein took place with substantial loss of tritium from C-3 and almost complete loss from C-2.